54 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



invaded by forest. The non-peat-making intervals must have lasted 

 more than 150 years, as appears from the size of the trees. The 

 region is now passing through another dry period and the peat bogs 

 are not increasing. De la Beche^^ has referred to the Drumkelin bog 

 in Donegal, Ireland, as affording a striking illustration of interrup- 

 tion in accumulation of peat. At 16 feet below the surface and rest- 

 ing on 15 feet of peat, a house was reached 12 feet square, 9 feet high 

 and constructed wholly of oak. When the peat had been removed 

 from about the house, a paved pathway was disclosed, leading to a 

 hearthstone covered with ashes. Near the house were stumps of oak 

 trees, which evidently were growing when the liouse was inhabited. 

 A layer of sand had been spread over the surface before the little 

 building was erected. This pause in growth of the deposit was of 

 sufficiently long duration to permit forest growth and to invite habita- 

 tion. It was followed by return of swamp conditions, during which 

 16 feet of peat accumulated. 



Geikie^* has recorded several cases of which only two need be 

 recalled here. At Strathcluony, three tiers of Scotch firs were seen, 

 separated by layers of peat. Several tiers were exposed in a railway 

 cutting across the Big Moss, one of standing firs with branching 

 roots at 6 feet below the surface, a second at 12 and a third at 16 feet 

 below the surface ; so that, counting the present surface growth, four 

 forests have grown there since the bog-making began ; that is to say, 

 the swamp conditions have been interrupted four times by periods of 

 lessened moisture, the last being the present. The preceding three 

 were succeeded by periods of wetness during which peat-making pro- 

 ceeded vigorously. It must not be supposed that even in the drier 

 periods accumulation of peat ceased wholly. It has been known a 

 long time that the offal of conifers can accumulate as peat. Reinsch^^ 

 says that in the Fichtelgebirge needles of Fichten, Tannen and Fohren 

 are important as peat-making material and that in time they accumu- 

 late in such quantity that a quaking bog is the result. One must in- 

 sist here that the mere accumulation of peaty materials around and 



53 H. T. de la Beche, "The Geological Observer," Amer. ed., 1851, p. 134. 



54 J. Geikie, " The Great Ice Age," 3d ed., London, 1895, pp. 286-293, 303. 



55 H. Reinsch, " Ueber den Torf des Fichtelgebirges," Joiirn. f. pr. Client., 

 Bd. XVI., 1839, p. 486. 



